Spin-valley lifetimes in a silicon quantum dot with tunable valley splitting

TL;DR

This study demonstrates tunable valley splitting in silicon quantum dots and investigates spin relaxation mechanisms, revealing long-lived spin states and a magnetic field-dependent relaxation rate influenced by valley and Zeeman splittings.

Contribution

It provides precise electrostatic control of valley splitting and uncovers the phonon-mediated spin relaxation process in silicon quantum dots.

Findings

Valley splitting tunable from 0.3 to 0.8 meV via gate control

Single-electron spin lifetimes exceeding 2 seconds

Spin relaxation rate shows a hot-spot when Zeeman and valley splittings match

Abstract

Although silicon is a promising material for quantum computation, the degeneracy of the conduction band minima (valleys) must be lifted with a splitting sufficient to ensure formation of well-defined and long-lived spin qubits. Here we demonstrate that valley separation can be accurately tuned via electrostatic gate control in a metal-oxide-semiconductor quantum dot, providing splittings spanning 0.3 - 0.8 meV. The splitting varies linearly with applied electric field, with a ratio in agreement with atomistic tight-binding predictions. We demonstrate single-shot spin readout and measure the spin relaxation for different valley configurations and dot occupancies, finding one-electron lifetimes exceeding 2 seconds. Spin relaxation occurs via phonon emission due to spin-orbit coupling between the valley states, a process not previously anticipated for silicon quantum dots. An analytical theory describes the magnetic field dependence of the relaxation rate, including the presence of a dramatic rate enhancement (or hot-spot) when Zeeman and valley splittings coincide.